1. Field of the Invention
The present invention relates to an on-board antenna.
2. Description of the Related Art
Conventionally, a planar antenna is known which comprises a radiation element provided on the same surface of, for example, an automotive window glass which is located on a passenger compartment side thereof and a substantially annular grounding conductor which surrounds the periphery of an outer edge portion of the radiation element at a position spaced away outwardly from the outer edge portion of the radiation element (for example, refer to Japanese Published Patent Application JP-A-2002-252520.
Incidentally, in installing the planer antenna according to the aforesaid conventional example on a vehicle, in the event that the planner antenna is installed on an automotive window glass such as a front windshield or rear window glass, for example, it is desired to prevent the antenna not only from interrupting the vision of occupants but also from deteriorating the external appearance of the vehicle.
However, in the event that the dimensions and layout of the planar antenna are regulated based on the external appearance of the vehicle, for example, there may be caused a risk that attaining desired transmitting and receiving properties is made difficult.
In addition, for example, in a case where a plurality of planar antennas having target frequency bands which are different from each other are installed on the vehicle, in the event that an interference action between the antennas becomes excessively large, there is caused a problem that obtaining desired transmitting and receiving properties becomes difficult.